Boris D. Vasin

On the formation of uranium(V) species in alkali chloride melts

Uranyl(V) species are normally unstable in solutions but are here shown to be stable in high-temperature chloride melts. Reactions leading to the formation of UO2Cl43– ions were studied, including thermal decomposition and chemical reduction of uranyl(VI) chloro-species in various alkali chloride melts (LiCl, 3LiCl–2KCl, NaCl–KCl, and NaCl–2CsCl) at 550–850 °C. Decomposition of UO2Cl42– species under reduced pressure, with inert gas bubbling through the melt or using zirconium getter in the atmosphere results in the formation of UO2Cl43– and UO2. Elemental tellurium, palladium, silver, molybdenum, niobium, zirconium, and hydrogen, as well as niobium and zirconium ions were tested as the reducing agents. The outcome of the reaction depends on the reductant used and its electrochemical properties: uranyl(VI) species can be reduced to uranyl(V) and uranium(IV) ions, and to uranium dioxide.

Behaviour of Rare Earth Elements in Molten Salts in Relation to Pyrochemical Reprocessing of Spent Nuclear Fuels

Electrochemical Society, Phys. Anal. Electrochem. Div.;Electrochemical Society, Electrodeposition Division;Electrochemical Society, High Temperature Materials Division;Electrochemical Society, Battery Division;Electrochemical Society, Energy Technology Division

Spectroelectrochemical study of molybdenum containing chloride melts

The behaviour of molybdenum(III) and (IV) ions in NaCl—2CsCl eutectic based melts at 550—750°C was studied using high temperature spectroelectrochemistry and cyclic voltammetry. Anodic oxidation of Mo(III) ions yields Mo(IV) containing melts. Mo(IV) — Mo(III) recharge is reversible. The values of the formal standard Mo(IV)/Mo(III) red-ox potential, ΔG of formation and mixing MoCl4 in NaCl—2CsCl at 550°C are estimated.

Effect of Melt Composition on the Reaction of Uranium Dioxide with Hydrogen Chloride in Molten Alkali Chlorides

The reaction of uranium dioxide with excess hydrogen chloride in alkali chloride melts (LiCl, 3LiCl-2KCl, NaCl-KCl and NaCl-2CsCl) has been studied between 450 and 750◦C, and the reaction products were characterized by electronic absorption and X-ray absorption spectroscopy. Uranium( V), [UO2Cl4]3−, and uranium(IV), [UCl6]2−, species were formed. They depended upon the temperature and the radius of the alkali cations present. Uranium(V) ions predominated in melts with small cations (LiCl and 3LiCl-2KCl).

Spectroelectrochemical Study of Neptunium in Molten LiCl-KCl Eutectic

Neptunium behaviour in an LiCl-KCl eutectic melt at 723 K was studied using spectroelectrochemistry. Cathodic reduction of neptunium(IV)-containing melts led to the formation of Np(III) ions and then neptunium metal. Electronic absorption spectra of Np(IV) and Np(III) chloro species in LiCl-KCl melt were recorded and resolved into individual Gaussian bands. The nature of neptunium complex ions in the melt is discussed.

The Effect of Fission Product Elements on the Behavior of Uranyl Species in Alkali Chloride Melts: a Contribution towards Reprocessing Spent Oxide Fuels

Currently the primary technology for reprocessing spent nuclear fuels is based on solvent extraction (PUREX process). One of the possible alternatives is pyrochemical reprocessing employing high temperature alkali metal chloride-based melts as the reaction media. There are a number of approaches that can be applied and these involve using melts containing chloro complexes of uranium in oxidation states (III) and (IV) and oxychloro complexes (uranyl) in oxidation states (VI) and (V). Uranyl containing melts can be used for precipitating UO2 or preparing MOX fuel. Fission product elements, as well as container materials in contact with the melt, can affect the speciation and behaviour of uranium.

Speciation of Rhenium in Chloride Melts: Spectroscopic and Electrochemical Study

Speciation of rhenium in high-temperature alkali chloride-based melts was studied using electronic absorption and IR spectroscopy of molten salts and diffuse reflectance spectroscopy of quenched melts. Rhenium was added to the melts by anodic dissolution of the metal (at anodic current densities of 0.005 - 0.05 A/cm2), by reacting Re and ReO2 with Cl2 and HCl, and by dissolving K2[ReCl6]. The melts included 3LiCl-2KCl and NaCl-2CsCl eutectics, an NaCl-KCl equimolar mixture, and pure NaCl, KCl and CsCl between 450 and 850 ◦C. Rhenium was present in the melts as Re(IV) hexachloro-ions, [ReCl6]2−; no evidence of species containing rhenium in oxidation states below four was obtained. The kinetics of [ReCl6]2− disproportionation in molten alkali chlorides were investigated, and the IR spectra of [ReO4]− ions in molten CsCl-CsI and CsI were measured for the first time.

The application of the spectroelectrochemical method in the studies of molybdenum, tungsten, and uranium in chloride melts

AbstractThe behavior of molybdenum(III), tungsten(IV), and uranium(VI) ions in NaCl-2CsCl-eutectic-mixture-based melt at 550°C is studied by spectroelectrochemical method. Anodic oxidation of MoCl63− and WCl62− yields melt-soluble chloride compounds MoCl62− and WCl6− respectively. It is shown that the electrochemical recharging in the Mo(III)/Mo(IV) system is reversible; the formal standard potential E*Mo(IV)/Mo(III)and the Gibbs energy

Electrochemical and Spectroscopic Properties of Technetium in Fused Alkali Metal Chlorides

\Delta G_{MoCl_4 (melt)}^*